I had the need to match a batch of transistor pairs for a project, so I designed a circuit board based on a circuit by Ian Fritz.

I had a little over one hundred transistors to sort thru, so I built up this small board just to match them.


The hardest part of this project was ordering the matched resistors used in the emitter to negative supply circuit. I thought that I had found the exact resistor network that I needed, but Digikey had an incorrect description of the part. It ended up being a 10K x 100K pair which is a total fail for this circuit. Be sure to check the part number against the manufactures specification sheet to verify you are ordering the part you need, instead of trusting the sellers part description.
What I finally ended up with was a Vishay MPMT2003AT1 resistor array with a ratio tolerance of ± 0.05 % and a ratio drift of ± 2 ppm/°C. It was supplied in a SOT-23 package, and needed to be soldered to a pin header to match the board socket.

With 100K Ohm resistors the current passing thru the emitter is around 0.126 mA, and by connecting a voltmeter to each of the emitters we can measure the differential emitter voltage of the two transistors.
Different values of matched emitter resistor pairs can be used to change the current passing thru the transistor, such as a 10K Ohm pair for around 1.2 mA of current. For fine adjustment the power supplies can be adjusted.
To see if there is any measurement mismatch caused by the matched resistors, the matched resistor pair module can be removed and rotated 180 degrees, while leaving the transistors in the same position, and then compare the measurements from both positions.

My plans are to mount the board in a small enclosure to prevent air currents from affecting the measurements, but still have easy access for changing out the transistors.
EagleCAD V7.7 Transistor tester dual rev. 1.0 schematic and board ZIP file